This invention relates to a fluid flow meter or sensor particularly adapted for measuring the flow rate of fuel to an internal combustion engine.
In fluid flow sensors previously developed, a continuous circular cavity or raceway was provided having an inlet to the fluid supply source and an outlet leading to the fluid using apparatus (e.g., an engine). A small ball supported by the fluid in the circular cavity moved with the fluid current in a continuous circular path, and on every lap of the circular path, the ball passed through a sensor element. Thus, every complete circuit of the ball around the circular path provided a measurable signal for computing the volume of fluid flow per unit of time. Such a flow sensor device is described in greater detail in U.S. Pat. No. 4,263,812, which is assigned to the same assignee as the present invention.
While the aforesaid arrangement cell was successful, it had inherent disadvantages and problems. For example, under certain conditions, such as a relatively low fuel flow rate (which often occurs with modern, economical engines), insufficient fluid force may be applied to the ball to keep it moving consistently with the fuel within its raceway. This low flow condition often resulted in false readings by the sensor element, thereby reducing the accuracy of the flow rate measurement. It was found that by reducing the size of the fluid inlet to the raceway, an increased force on the circulating ball could be obtained, but at higher flow rates, excessive back pressure was created which also decreased the accuracy of the flow meter. Thus, the problem arose of providing an improved flow meter capable of increased performance and greater reliability, and particularly one that would produce accurate measurements for fluid flow within the entire range of relatively low flow rate to relatively high flow rate.
It is, therefore, a general object of the present invention to provide an improved fluid flow meter that solves the aforesaid problems.
Another object of the invention is to provide a flow meter or sensor that is more sensitive and more accurate, particularly at relatively low rates.
Another object is to provide a flow meter that is rugged, reliable, and particularly well adapted for ease and economy of manufacture.
Another more specific object of the present invention is to provide an improved fluid meter for measuring fluid flow rates of the type wherein a circulating ball moves with the fluid in a continuous raceway and that utilizes means at the inlet to the raceway for providing a relatively small opening at low flow rates and a relatively large opening at high flow rates, so that despite the rate of fluid flow, there is always sufficient force on the ball to keep it circulating within the fluid in the raceway and yet no excess back pressure is produced at high flow rates.
Another object of the invention is to provide a fluid meter for an internal combustion engine having an oval raceway with a circulating ball and a nozzle means in the inlet to the raceway which will provide a fluid meter for an internal combustion engine having an oval raceway with a circulating ball and a nozzle means in the inlet to the raceway which will provide a relatively small opening for the fluid at low flow rates and will automatically provide a larger opening at relatively high flow rates, so that adequate fluid force on the ball is produced to keep it moving smoothly and excessive back pressure is avoided throughout the entire range of fuel flow rates for the engine.